Maclin went down at the end of a non-contact drill and appeared in pain while on the ground for several minutes. He was helped onto the cart and needed assistance getting off it and going into the team's practice facility.

"Appreciate all the love and support twitter fam....sad day but I have setbacks my entire life. Minor setback for a MAJOR comeback! (hash)birdgang," he wrote on Twitter.

Philadelphia is in its second full practice under new coach Chip Kelly. The first practice with pads is Sunday.

The Eagles signed wide receiver David Ball to the 90-man roster. The 29-year-old Ball played for Kelly at New Hampshire, and broke Jerry Rice's Division I-AA record for touchdown receptions. Ball spent time in training camp with Chicago and the New York Jets in 2007-08.

Maclin is headed into his fifth season with the Eagles. He led the team with 69 catches for 857 yards and seven touchdowns last season, and the former first-round pick is in the final year of his rookie contract.

Two-time Pro Bowl wide receiver DeSean Jackson is Philadelphia's other starter. The team has veterans Jason Avant and Riley Cooper along with several younger wideouts in camp.

Maclin has averaged 64 catches, 863 yards and six TDs in his first four seasons. His best year was in 2011 when he had 70 receptions for 964 yards and 10 TDs.